1. Field of the Invention
The present invention relates to a relay station, a radio base station, and a communication method between these stations for utilizing radio communication. The present invention is suitably used for addition of relay stations on the basis of the radio communication system specified, for example, in IEEE802.16.
2. Description of the Related Art
A radio communication system to realize communication via a radio communication path is now spreading in the world-wide scale as a representative system of the WCDMA and CDMA 2000 or the like. In this radio communication system, a plurality of radio base stations are provided for service areas and a radio terminal makes communication with the other communication devices (communication terminals) via any of the radio base stations. Moreover, in such system, a service area formed by a base station is overlapped with another service area formed by an adjacent base station. Therefore the communication can be maintained by a handover process even though radio environment of the communication gets worse.
Moreover, as a radio system, a technology for example, code division multiplex, time division multiplex, frequency multiplex, and OFDM (OFDMA) or the like is employed and thereby a plurality of radio terminals can be connected simultaneously to a radio base station.
However, a radio terminal is sometimes located in the area out of the service area where a radio base station can make radio communication. In this case, a radio terminal cannot receive radio signals from a radio base station and cannot receive the service. Therefore, a system has been proposed, wherein relay stations are allocated within the area for making radio communication with a radio base station and the radio terminal and the radio base station can make radio communication via a relay station.
Particularly, the task group of 802.16j is now discussing introduction of such relay station (RS).
Matters in relation to the IEEE802.16 are disclosed, for example, in the IEEE Std802. 16TM-2004 and the IEEE Std802. 16eTM-2005.